Tank cavity resonator for use in high frequency oscillator

ABSTRACT

A tank cavity resonator, including plate tuning capacitance, plate blocking capacitance, and tank inductance, for use in high frequency (e.g. UHF) oscillators, comprises a pair of concentric metallic cylinders, an outer and an inner cylinder, closed at one end by a common baseplate. A planar, three-layer (metalinsulator-metal), member forming the plate blocking capacitor contacts the other end of the inner cylinder and is spaced from a movable planar metallic member which contacts the other end of the outer cylinder, thereby forming a variable plate tuning capacitor. The tank inductance is formed by the current path which includes the outer surface of the inner cylinder, the upper surface of the baseplate and the inner wall of the outer cylinder.

United States Patent 1 3,573,658

[72] Inventors George R. Hair [56] References Cited Clifton, NJ; FOREIGN PATENTS John G. Nielsen, Wantagh, N.Y.

l N 806 544 683,894 9/l949 Great Britain 331/94 i l d 0. Mar 12, 1969 Primary Examiner-John Kominski [45] Patented Apr. 6, 1971 Attorney-Ryder, McAnlay & Hefter [73] Assignee Bondit Corp. Newark, NJ.

ABSTRACT: A tank cavity resonator, including plate tuning capacitance, plate blocking capacitance, and tank inductance, for use in high frequency (e.g. UHF) oscillators, comprises a pair of concentric metallic cylinders, an outer and an inner cylinder, closed at one end by a common baseplate. A planar, [54] TANK CA RESONATOR FOR USE IN HIGH three-layer (metal-insulator-metal), member forming the FREQUENCY OSCILPATOR plate blocking capacitor contacts the other end of the inner 10 Cl8 Drawing Flgscylinder and is spaced from a movable planar metallic [52] US. Cl 331/96, member which contacts the other end of the outer cylinder, 33 1/97 thereby forming a variable plate tuning capacitor. The tank in- [51] Int. Cl H03b 5/10 ductance is formed by the current path which includes the [50] Field of Search 331/96, 97, outer surface of the inner cylinder, the upper surface of the 98 baseplate and the inner Wall of the outer cylinder.

022 39 C24 4/ T0 a/e/o 7o RESISTOR 1F F' I? L28 r L30 67 as 1, j E I /5a /6b' v 45 g 1- sun 70 0.6. PLATE VOLTAGE Patented April 6, w?!

2 Sheets-Sheet 1 55:3? gull] 1113b v S 252% m3 Ww 8l 2x :m 3 Ad l lm 3w ril- GEORGE R. HAIR JOHN G. NIELSEN ATTORNEY Patented April 6, MN 3,573,5

2 Sheets-Sheet 2 FIG. 2 L32 T0 GRID RESISTOR 7'0 0.6. PLATE VOL7I4GE v FIG. 3

54 70 CATHODE PLANE 72- 22 C24 WVENTORS: GEORGE R. HAIR JOHN G. N/EL SEN A TTORNEV TANK CAVITY RESONATOR FOR USE IN HIGH FREQUENCY OSCILLATOR BACKGROUND OF THE INVENTION This invention relates to tank cavity resonators for use in high frequency oscillators and, more particularly, to a high-efficiency UHF tank cavity, for use in dielectric heating, in which the reactive components of the cavity are an integral part of the apparatus.

A recently developed dielectric heating apparatus and procedure is disclosed in Ser. No. 653,787 of M. Goldstein et al. filed on Jul. 17, 1967 and assigned to applicants assignee. In accordance with that application layers of sheet material are joined by means of a thermally active adhesive between the layers. The material and the adhesive are fed into an apparatus which concurrently compresses the material together and subjects it to the field developed by radiofrequency heating apparatus. The field is applied by means of a pair of spaced electrodes through which the material and adhesive pass, the gap between the electrodes being controllablein order that the electrodes may concurrently apply a compressive pressure to the material and adhesive.

In many applications of dielectric heating, such as the aforementioned, the maximum amount of power which can be ap plied to the work load (i.e., the materials and adhesive) is limited by the breakdown voltage of the material. However, the power delivered to the work load is proportional to Bf, E

being the electric field which is proportional to voltage and f being the operating frequency. It is, therefore, possible to'attain higher power levels at the same electrode voltage (below breakdown) by increasing the operating frequency of the oscillator which generates the electric field.

It is well known in the art that conventional oscillator designs, when used in circuits operating above MHz. result in a significant reduction in efficiency. Low efficiency occurs because at higher frequencies the tank cavity reactance decreases thereby increasing the amplitude of the circulating currents in the resonator. Consequently, the FR losses in the tank coil, tank capacitor and interconnections limit the power which can be delivered to the work load.

Another problem which'arises in conventional oscillators is frequency instability due to variations in load capacitance. Such variations occur in the aforementioned dielectric heating apparatus as a result of continuous changes in electrode spacing with variation in the thickness of sheet materials introduced between the electrodes. Because the electrode spacing forms part of the tank cavity capacitance, variations in spacing produce variations in operating frequency. An unstable operating frequency is disadvantageous in that radiation outside of the intended frequency channel could cause interference with other communications systems.

It is, therefore, one object of the present invention to increase the power deliverable to a workload by means of a high frequency oscillator.

It is a more specific object of this invention to increase such power by increasing the operating frequency of the oscillator but without increasing the applied voltage beyond the breakdown voltage of the work load.

It is another object of this invention to increase the operating frequency without concurrent reduction in efficiency.

It is still another object of this invention to increase the frequency stability of a high frequency oscillator.

SUMMARY OF THE INVENTION These and other objects are accomplished in an illustrative embodiment of the invention which comprises a tank cavity resonator, including a plate tuning capacitance, plate blocking capacitance and tank inductance, for use in high frequency (e.g. UHF) oscillators. The resonator includes a pair of concentric metallic cylinders, an outer and an inner cylinder, closed at one end by a common base plate. A planar, threelayer (metal-insulator-metal), member forming the plate blocking capacitor contacts the other end of the inner cylinder and is spaced from a movable planar metallic member which contacts the other end of the outer cylinder, thereby'forming a variable plate tuning capacitor. The tank inductance is formed by the current path which includes the outer surface of the inner cylinder, the upper surface of the baseplate and the inner wall of the outer cylinder.

As a result of the fact that the resonator capacitance and inductance are an integral part of the apparatus, the resonator (in combination with an appropriate drive circuit) is capable of operation at frequencies in the UHF band (e.g. MHz.) with efficiencies in excess of 90 percent.

Furthermore, the resonator design results in improved frequency stability because the resonator circuit is equivalent to a tank circuit with high capacitance so that changes in workload capacitance (e.g. electrode spacing) have little effect on the total capacitance and hence little effect on the operating frequency. In addition; the resonator is self-shielding due to its closed-in integral construction. Therefore, spurious radiation is reduced. This feature, and the increased frequency stability, combine to reduce interference with other communications systems.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects of the invention, together with its various features and advantages, can be easily understood from the following more detailed discussion, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit drawing of a high frequency oscillator showing schematically a tank cavity resonator in accordance with an illustrative embodiment of the invention;

FIG. 2 is a partial cross-sectional side view of a high frequency oscillator as shown in FIG. 1; and

FIG. 3 is a partial top view of the embodiment shown in FIG. 2.

DETAILED DESCRIPTION Before describing in detail the construction of the tank resonator in accordance with the invention, it will be helpful to consider first a high frequency oscillator circuit as shown in FIG. 1. The oscillator circuit comprises a triode 10 having one terminal 14d of its grid 14 connected to ground through the parallel combination of a feed through capacitor C37 and a grid resistor R18. Two other grid terminals and Me are also connected to ground through bypass capacitors C200 and C20 respectively. Each side (16a and 16b) of the filament 16 is RF insulated from ground by filament choke L28 and L30, respectively. Bypass capacitors C34 and C36 assure the RF isolation of the filament. The points 33 and 35 between each series connection are connected to a source of filament voltage, not shown, typically a 6-volt AC supply. In addition, each side (16a and 16b) of the filament 16 is connected through a capacitor (C22 and C24) to one side of a tuning circuit which comprises an inductor L32 in parallel with a variable capacitor C26, the other side of the parallel combination being grounded.

Between the plate12 and ground is connected a tank cavity resonator 50 which comprises a plate tuning capacitor C42 connected between plate 12 and ground, and the series combination of plate blocking capacitor C44 and inductor L46 also connected between the plate and ground. The output to the bonding machine 80 of the Goldstein et al. disclosure is coupled from the tank cavity via coupling inductor L48 located in magnetic proximity to tank inductor L46. In particular, the high-voltage side of L48 is connected to the lower of the pair of electrodes used in the bonding machine to compress materials to be joined and to apply an RF field thereto; the upper electrode is typically grounded. As mentioned previously, the field causes a thermally .active adhesive between the materials to liquefy or plasticize and subsequently to solidify and thereby bond the materials together. The disclosure of the aforementioned Goldstein et al. application is incorporated herein by reference as if fully disclosed herein.

The mode of operation of the oscillator is well known in the art, and, for the purposes of simplicity will not be repeated here except to indicate that the actual construction and tuning of resonator 50 determines the operating frequency, frequency stability, efficiency and isolation of the oscillator.

A resonator construction in accordance with an illustrative embodiment of the invention is shown in FIGS. 2 and 3 where numerals corresponding to FIG. 1 have been used to indicate identical components. The resonator is constructed, as previously mentioned, so that its associated capacitance and inductance form an integral part of the tank design. In particular, the tank resonator 50, including its plate tuning capacitance C42, plate blocking capacitance C44 and tank inductance L46, comprises a pair of concentric metallic cylinders 52 and 54, closed at one end by a common baseplate 56. A planar, three-layer, member C44 contacts the other end of inner cylinder 52 thereby forming the blocking capacitance. The three layers include a pair of metallic planar members 440 and 44b between which is sandwiched an insulative layer 440 (e.g., a Teflon layer). The metallic member 44b contacts the upper end of inner cylinder 52. Member 44b is connected to the plate of triode 10, through conical member 62 which has at its apex cylindrical spring finger contacts 64 for receiving the anode contact 12a of triode 10. During tuning of the plate circuit, the tube anode extension moves inside the spring finger contacts. A connector 60 contacts the conical member 62 and passes through a hole in baseplate 56 to a source of DC plate voltage, not shown. In addition, the RF bypass capacitor C58 is connected between the connector 60 and the baseplate 56. Due to the electrical partitioning of the resonator, a plate choke is not needed.

The plate blocking capacitor C44, which has an aperture for permitting the insertion therethrough of triode l and a portion 45 which extends beyond the wall of inner cylinder 52, is spaced from a movable metallic ground plane 66 having a flange 68, upon which are mounted a ring of spring fingers 67 which are in contact with the inner wall 540 of outer cylinder 54, thereby forming an integral plate tuning capacitor (C42 of FIG. I). The tank inductance (L46 of FIG. 1) is also integral to the structure, being formed by the current path which includes the outer surface 520 of inner cylinder 52, the upper surface 56a of baseplate 56 and the inner wall 540 of outer cylinder 54. The frequency of operation is controlled by changing the spacing between ground plane 66 and the extended portion 45 of capacitor C44. The output power is taken from the resonator by means of coupler 480 which includes a coupling loop 49 located between the inner and outer cylinders. Load impedance can be optimized by changing the position of the coupling loop 49 between the two cylinders.

The remaining structure of the oscillator, as shown in FIGS. 2 and 3, includes a housing 70 afiixed to the ground plane 66 and into which extends the socket end of triode 10. The grid resistor R18 (FIG. 1) is connected through feed-through capacitor C37 (FIGS. 1 and 3) to the grid pin 14d of triode via connector 41. Within the housing is included a socket a socket plate 39 to which are connected filament bypass capacitors C22 and C24, the latter also being connected to cathode pins 160 and 16b, respectively. Grid coil L32 is also connected to plate 39. The filament chokes L28 and L30 connect filament pins 16a and 16b to the filament feed-through bypass capacitorsC34 and C36 (FIG. 3). Some of this construction is depicted in FIG. 3 as well, which shows in addition, grid bypass capacitors C and C204: connected between grid pins 140 and 14e of socket 39 and trapezoidal member 43.

Grid tuning capacitor C26 is connected to member 43 and to cathode plane 72.

The following parameters are given for the purposes of illustration only and are not to be construed as limitations upon the scope of the invention. A 100 MHz. oscillator as shown in FIG. I typically has parameter values as shown in table 1.

TABLE I Tube 10 --code 5867A R18 -3,300 ohms C20 and C20a -50 picofarads C22 picofarads C24 100 picofarads C26(range) -2 l0 picofarads C34 ---0.001 microfarads C36 -0.00l microfarads C37 l 00,picofarads C42(range) 73O picofarads C44 100 picofarads L28 --50 microhenries L30 ---50 microhenries L32 -l microhenries L46 -0.4 microhenries L48 -0.5 microhenries It is to be understood that the above-described arrangements are merely illustrative of the many possible specific embodiments which can be devised to represent application of the principles of the invention. Numerous and varied other arrangements can be devised in accordance with these principles by those skilled in the art without departing from the spirit and scope of the invention.

We claim:

1. For use in a high frequency oscillator a cavity resonator, including a tuning capacitor in parallel with the series combination of a blocking capacitor and an inductor, comprising:

an outer metallic cylinder;

an inner metallic cylinder disposed concentrically within said outer cylinder;

a metallic baseplate contacting one common end of each of said cylinders;

a planar blocking capacitor contacting the other end of said inner cylinder; and

a movable planar metallic member contacting the inner wall of said outer cylinder and being spaced in parallel relation to said blocking capacitor, thereby to form said tuning capacitor, said inductor being formed by the outer surface of said inner cylinder, the inner surface of said baseplate, and the inner surface of said outer cylinder.

2. The resonator of claim 1 wherein said planar blocking capacitor has a planar portion thereof which extends beyond the outer wall of said inner cylinder.

3. The resonator of claim I wherein said planar blocking capacitor comprises:

a first metallic planar member contacting the other end of said inner cylinder;

an insulative planar layer disposed on said first member; and

a second metallic planar member disposed on said insulative layer.

4. The resonator of claim 3 wherein said oscillator includes a vacuum tube having an external anode cap, and wherein said blocking capacitor has an aperture for the insertion therethrough of said tube, and in combination with a conical member contacting at its open end said second planar member and having at its apex a contact for receiving said anode cap.

5. The resonator of claim 1 for use in a high frequency oscillator for bonding together layers of sheet material via a thermally active adhesive therebetween in combination with bonding apparatus comprising:

a pair of spaced electrodes through which said materials and adhesive is passed, said electrodes being electrically coupled to the output of said resonator so as to generate an electric field in said materials and said adhesive; and

means for controlling the spacing of said electrodes so as to apply a compressive pressure to said materials and said adhesive concurrently with the application of said electric field, thereby to cause said adhesive to liquefy and subsequently upon solidification of said adhesive to bond said materials together.

6. For use in a high frequency oscillator for bonding together layers of sheet material via a thermally active adhesive therebetween, a cavity resonator, including a tuning capacitor in parallel with the series combination of a blocking capacitor and an inductor, comprising:

an outer metallic cylinder;

an inner metallic cylinder disposed concentrically within said outer cylinder;

a metallic baseplate contacting one common end of each of said cylinders; and

a planar blocking capacitor contacting the other end of said inner cylinder and having a planar portion thereof which extends beyond the outer wall of said inner cylinder, said capacitor comprising:

a first metallic planar member contacting the other end of said inner cylinder; I

an insulative planar layer disposed on said first member;

a second metallic planar member disposed on said insulative layer;

said oscillator including a vacuum tube having an aperture for the insertion therethrough of said tube;

a conical member contacting at its open end said second planar member of said blocking capacitor and having at its apex a contact for receiving said anode cap; and

a movable planar metallic member contacting the inner wall of said outer cylinder and being in spaced parallel relation to said blocking capacitor, thereby to form said tuning capacitor, said inductor being formed by the outer surface of said inner cylinder, the inner surface of said baseplate and the inner surface of said outer cylinder.

7. A high frequency oscillator for use in apparatus for bonding together layers of sheet material via a thermally active adhesive therebetween comprising:

a vacuum tube triode having anode, cathode and grid electrodes;

means for applying filament voltage to said cathode electrode;

means for biasing said grid electrode; and

a tank cavity resonator connected between said anode electrode and ground for varying the operating frequency of said oscillator, said resonator comprising:

an outer metallic cylinder;

an inner metallic cylinder disposed concentrically within said outer cylinder;

a metallic baseplatecontacting one common end of each of said cylinders;

a planar blocking capacitor contacting the other end of said inner cylinder; and

a movable planar metallic member contacting the inner wall of said outer cylinder and being in spaced parallel relation to said blocking capacitor, thereby to form a tuning capacitor, the outer surface of said inner cylinder, the inner surface of said baseplate, and the inner surface of said outer cylinder forming an inductor in series with said blocking capacitor, theseries combination being in parallel with said tuning capacitor.

8. The oscillator of claim 7 wherein said planar blocking capacitor has a planar portion thereof which extends beyond the outer wall of said inner cylinder. 1

9. The oscillator of claim 7 wherein said planar blocking capacitor comprises:

a first metallic planar member contacting the other end of said inner cylinder;

an insulative planar disposed on said first member; and

a second metallic planar member disposed on said insulative layer.

10. The oscillator of claim 9 wherein said vacuum tube is contained within an envelope having an external anode cap connected to said anode electrode, and wherein said blocking capacitor has an aperture for the insertion therethrough of said tube, and in combination with a conical member contacting at its open end said second planar member and having at its apex a contact for receiving said anode cap. 

1. For use in a high frequency oscillator a cavity resonator, including a tuning capacitor in parallel with the series combination of a blocking capacitor and an inductor, comprising: an outer metallic cylinder; an inner metallic cylinder disposed concentrically within said outer cylinder; a metallic baseplate contacting one common end of each of said cylinders; a planar blocking capacitor contacting the other end of said inner cylinder; and a movable planar metallic member contacting the inner wall of said outer cylinder and being spaced in parallel relation to said blocking capacitor, thereby to form said tuning capacitor, said inductor being formed by the outer surface of said inner cylinder, the inner surface of said baseplate, and the inner surface of said outer cylinder.
 2. The resonator of claim 1 wherein said planar blocking capacitor has a planar portion thereof which extends beyond the outer wall of said inner cylinder.
 3. The resonator of claim 1 wherein said planar blocking capacitor comprises: a first metallic planar member contacting the other end of said inner cylinder; an insulative planar layer disposed on said first member; and a seCond metallic planar member disposed on said insulative layer.
 4. The resonator of claim 3 wherein said oscillator includes a vacuum tube having an external anode cap, and wherein said blocking capacitor has an aperture for the insertion therethrough of said tube, and in combination with a conical member contacting at its open end said second planar member and having at its apex a contact for receiving said anode cap.
 5. The resonator of claim 1 for use in a high frequency oscillator for bonding together layers of sheet material via a thermally active adhesive therebetween in combination with bonding apparatus comprising: a pair of spaced electrodes through which said materials and adhesive is passed, said electrodes being electrically coupled to the output of said resonator so as to generate an electric field in said materials and said adhesive; and means for controlling the spacing of said electrodes so as to apply a compressive pressure to said materials and said adhesive concurrently with the application of said electric field, thereby to cause said adhesive to liquefy and subsequently upon solidification of said adhesive to bond said materials together.
 6. For use in a high frequency oscillator for bonding together layers of sheet material via a thermally active adhesive therebetween, a cavity resonator, including a tuning capacitor in parallel with the series combination of a blocking capacitor and an inductor, comprising: an outer metallic cylinder; an inner metallic cylinder disposed concentrically within said outer cylinder; a metallic baseplate contacting one common end of each of said cylinders; and a planar blocking capacitor contacting the other end of said inner cylinder and having a planar portion thereof which extends beyond the outer wall of said inner cylinder, said capacitor comprising: a first metallic planar member contacting the other end of said inner cylinder; an insulative planar layer disposed on said first member; a second metallic planar member disposed on said insulative layer; said oscillator including a vacuum tube having an aperture for the insertion therethrough of said tube; a conical member contacting at its open end said second planar member of said blocking capacitor and having at its apex a contact for receiving said anode cap; and a movable planar metallic member contacting the inner wall of said outer cylinder and being in spaced parallel relation to said blocking capacitor, thereby to form said tuning capacitor, said inductor being formed by the outer surface of said inner cylinder, the inner surface of said baseplate and the inner surface of said outer cylinder.
 7. A high frequency oscillator for use in apparatus for bonding together layers of sheet material via a thermally active adhesive therebetween comprising: a vacuum tube triode having anode, cathode and grid electrodes; means for applying filament voltage to said cathode electrode; means for biasing said grid electrode; and a tank cavity resonator connected between said anode electrode and ground for varying the operating frequency of said oscillator, said resonator comprising: an outer metallic cylinder; an inner metallic cylinder disposed concentrically within said outer cylinder; a metallic baseplate contacting one common end of each of said cylinders; a planar blocking capacitor contacting the other end of said inner cylinder; and a movable planar metallic member contacting the inner wall of said outer cylinder and being in spaced parallel relation to said blocking capacitor, thereby to form a tuning capacitor, the outer surface of said inner cylinder, the inner surface of said baseplate, and the inner surface of said outer cylinder forming an inductor in series with said blocking capacitor, the series combination being in parallel with said tuning capacitor.
 8. The oscillator of claim 7 wherein said planar blocking capacitor has a planar portion thereof Which extends beyond the outer wall of said inner cylinder.
 9. The oscillator of claim 7 wherein said planar blocking capacitor comprises: a first metallic planar member contacting the other end of said inner cylinder; an insulative planar disposed on said first member; and a second metallic planar member disposed on said insulative layer.
 10. The oscillator of claim 9 wherein said vacuum tube is contained within an envelope having an external anode cap connected to said anode electrode, and wherein said blocking capacitor has an aperture for the insertion therethrough of said tube, and in combination with a conical member contacting at its open end said second planar member and having at its apex a contact for receiving said anode cap. 